In the processing of molten metals, it is desirable and often necessary to remove various solid impurities. In the production of steel, for example, molten steel is deoxidized, or "killed", by the addition of aluminum and silicon to scavenge dissolved oxygen, resulting in the formation of alumina and silica particles, known as inclusions, which must be removed from the molten batch. Filters of various kinds and compositions are used for this purpose. Open-celled ceramic structures in the form of replicas of organic sponges are described in U.S. Pat. No. 3,090,094 for use as molten-metal filters. Ceramic materials used in these filters are, for example, zirconia, zircon, petalite, mullite, talc, silica, and alumina. Foamed ceramic filters for molten metal processing are described, for example, in U.S. Pat. No. 3,893,917 to Pryor, et.al. Ceramic materials used in such filters are, for example, alumina, chromia, zirconia, magnesia, silica, and titania. The utility of such replica and foamed ceramic filters in molten metal service, however, is diminished by their fragility and inherent structure. Replica and foamed ceramics do not have sufficient strength for use in large filters, which limits the rate at which metal can be processed. Filters made of such replicas and foams have a random pore structure, which also does not permit desirable throughput rates of the molten metal.
Zircon-based refractory articles are known to have appreciable strength and corrosion resistance, and have been used in molten metal processing. For example, U.S. Pat. No. 3,303,032 issued to Holt, et.al. discloses refractory compositions of zircon and a basic oxide used as the lining of vessels, furnaces, or piping which come into contact with molten steel. U.S. Pat. Nos. 3,791,834 and 3,804,649, both issued to Manigault, disclose refractory compositions of zircon, titanium dioxide, and another oxide which can be used in contact with molten metal or glass. Molten-metal filters of monolithic honeycomb character, with multiple substantially parallel open channels, or longitudinally-extending cells therethrough, however, are not known to have been based on zircon.
It is therefore an object of this invention to provide a filter which has the strength and thermal shock resistance necessary for molten metal service and which has a configuration that allows sufficient flow of the molten metal therethrough.